This paper presents the optimization of a solar-powered humidification–dehumidification (HDH) desalination system for remote areas where it is assumed that only minimal external electric power (for operating control systems and auxiliaries) is available. This work builds on a previous system by disconnecting the condenser from the saline water cycle and by introducing a solar air heater (SAH) to further augment the humidification performance. In addition, improved thermal simulation models for the condenser and the humidifier are used to obtain more accurate productivity estimations. The heuristic gradient projection (HGP) optimization procedure is also refactored to reduce the number of function evaluations, to reach the minimum unit cost of produced fresh water, compared to genetic algorithms (GAs). A case study which assumes a desalination plant on the Red Sea near the city of Hurghada, Egypt, is presented. The optimum systems are shown to significantly reduce the unit cost of fresh water production below the reported minimum ($1.3/m3 compared to $3/m3), while keeping specific energy consumption within the reported range, 120–550 kWh/m3, for solar HDH systems.